Acute shifts in baroreflex control of renal sympathetic nerve activity induced by REM sleep and grooming in rats

The present study aimed to determine the impact of REM sleep and grooming on the baroreflex stimulus-response curve for renal sympathetic nerve activity (RSNA). At least 3 days before study, Wistar female rats (n = 12) were chronically implanted with catheters to measure systemic arterial pressure (P-a) and to intravenously infuse vasoactive drugs. In addition, electrodes were placed for measurements of RSNA, electroencephalogram, trapezius electromyogram and electrocardiogram. The baroreflex curve for RSNA was determined by changing P-a using rapid intravenous infusions of phenylephrine and nitroprusside and then fitted to an inverse sigmoid function curve. REM sleep induced a vertical suppression of the P-a-RSNA baroreflex curve, which was characterized by significant decreases in the maximum response (by 72.0%, P < 0.05) and the maximum gain (by 4.02% mmHg(-1), P < 0.05) compared with NREM sleep level. Grooming shifted the Pa-RSNA baroreflex curve upward and to the right, which was associated with increases in the maximum response (by 45.2%, P < 0.05), the minimum response (by 20.7%, P < 0.05) and the pressure at the centring point (by 11.1 mmHg, P < 0.05). These data suggest that the P-a-RSNA baroreflex curve was shifted acutely and differently in a state-dependent manner during natural sleep and wake cycle in rats.